US3982937A - Electrophotographic recording material - Google Patents

Electrophotographic recording material Download PDF

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Publication number
US3982937A
US3982937A US05/488,212 US48821274A US3982937A US 3982937 A US3982937 A US 3982937A US 48821274 A US48821274 A US 48821274A US 3982937 A US3982937 A US 3982937A
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United States
Prior art keywords
layer
selenium
article
tellurium
condensation product
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Expired - Lifetime
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US05/488,212
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English (en)
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Wolfgang Wiedemann
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Hoechst AG
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Hoechst AG
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording-members for original recording by exposure, e.g. to light, to heat or to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/02—Charge-receiving layers
    • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
    • G03G5/06—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor characterised by the photoconductive material being organic
    • G03G5/0622—Heterocyclic compounds
    • G03G5/0644—Heterocyclic compounds containing two or more hetero rings
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G5/00—Recording-members for original recording by exposure, e.g. to light, to heat or to electrons; Manufacture thereof; Selection of materials therefor
    • G03G5/02—Charge-receiving layers
    • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
    • G03G5/043—Photoconductive layers characterised by having two or more layers or characterised by their composite structure
    • G03G5/0436—Photoconductive layers characterised by having two or more layers or characterised by their composite structure combining organic and inorganic layers

Definitions

  • This invention relates to an article, suitable for use as electrophotographic recording material, comprising an electrically conductive carrier material, optionally provided with an intermediate layer, and a photoconductive layer.
  • a layer of an inorganic material such as selenium, selenium-tellurium, cadmium sulfide, or cadmium selenide having a thickness of less than 0.1 ⁇ m on an electrically conductive carrier material may act as a charge carrier injection layer for inorganic or organic charge carrier transport layers located above it.
  • Proposals of this type have been made in German Pat. No. 1,022,091, German Auslegeschrift No. 1,277,016, and German Offenlegungsschriften Nos. 1,964,817, 2,128,584, 2,128,641, and 2,165,295.
  • Inorganic transport materials considered in the above-mentioned specifications are, above all, relatively thick layers of amorphous selenium.
  • an inorganic charge carrier transport layer of, for example, selenium special light exposure arrangements are necessary because of the opacity of this material.
  • such materials are insufficiently flexible.
  • organic photoconductors for a transport layer As regards organic photoconductors for a transport layer, a proposal has been made to use substances possessing a polymeric structure, especially polyvinyl carbazole or the halogenated derivatives thereof. However, it has been found that layers of such polymer compounds cannot be employed by themselves since they lack a certain flexibility, which is necessary for good adhesion. On the other hand, there is a limit to the extent to which the polymeric compounds can be blended with resin binders; this is because of the turbidity which results and because of the observed increased residual charge relative to the base material.
  • a proposal also has been made to use double layers by locating a photoconductive layer above an organic insulating resin layer on an electrically conductive carrier material in an electrophotographic image exposure system employing the reflection principle, with a positive charge (German Offenlegungsschrift No. 1,622,364).
  • a photoconductive layer above an organic insulating resin layer on an electrically conductive carrier material in an electrophotographic image exposure system employing the reflection principle, with a positive charge (German Offenlegungsschrift No. 1,622,364).
  • such a process is suitable only for use with very special copying apparatuses, since the exposure is made through the carrier material only.
  • the very thin outer photoconductive layer causes severe wear of the photoconductor material.
  • the present invention provides an article which comprises an electrically conductive carrier layer, a layer comprising selenium or selenium-tellurium, and, on the side of the selenium or selenium-tellurium layer remote from the carrier layer, a layer comprising an oligomeric condensation product of 3-bromopyrene and formaldehyde having a degree of polymerization of 6 to 10.
  • the selenium or selenium-tellurium layer and the layer comprising the condensation product form a photoconductive double layer, wherein the layer comprising the condensation product can function as a charge carrier transport layer.
  • the various layers in the article of the invention preferably are continuous.
  • the invention makes it possible to provide highly photosensitive double layers which substantially overcome the disadvantages described above and are suitable for use in the xerographic copying process.
  • the materials of the invention may be made from easily accessible substances which are readily compatible with other substances, have good adhesion between the various layers, and combine high mechanical stability with adequate flexibility. They can without difficulty be located on a cylindrical drum or be processed as a continuous strip without showing special wear phenomena, since they are, in particular, vary abrasion-resistant. Even when unavoidable wear of the outer layer takes place, the photoconductive double layer system is not substantially impaired since, though abrasion causes a slight decrease of the thickness of the charge carrier transport layer and hence of the chargeability, the photosensitivity increases as a result of the decrease in thickness.
  • the electrophotographic recording material according to the invention is very particularly suitable for use in electrophotographic copying apparatuses.
  • the invention through using the compound which is easily accessible in accordance with U.S. Pat. No. 3,842,038, permits much broader applications.
  • FIGS. 1 and 2 of the accompanying drawings The construction of electrophotographic recording material according to the invention is shown, by way of example only, in FIGS. 1 and 2 of the accompanying drawings.
  • FIG.1 shows a material which is composed of an electrically conductive carrier layer 1, a vapor-deposited Se or Se/Te layer 2, and a charge carrier transport layer 3.
  • a plastic layer 4 having a layer 1 of metal thereon is provided as the carrier layer, onto which is applied an intermediate layer 5 which prevents charge carrier injection in the dark.
  • an intermediate layer 5 which prevents charge carrier injection in the dark.
  • a photoconductive double layer comprising a selenium or selenium/tellurium layer 2, and a charge carrier transport layer 3.
  • Suitable electrically conductive carrier materials include materials which previously have been proposed for this purpose.
  • the carrier materials to be used according to the invention include, for example, aluminum foils and optionally transparent bases, for example plastic materials which have been vapor-coated or laminated with aluminum, gold, copper, zinc, cadmium, indium, antimony, nickel or tin. Quite generally, any carrier material which has been rendered sufficiently electrically conductive can be employed.
  • an intermediate layer which comprises, for example, an organic material or a thermally-, anodically-, or chemically- produced metal oxide layer, for example an aluminum oxide layer, can be provided on the electrically conductive carrier material.
  • the purpose of such an intermediate layer is generally to lower the charge carrier injection from the electrically conductive carrier material into the selenium layer. Furthermore, it may favorably influence the adhesion between the carrier material and the selenium layer.
  • materials which undergo little surface dissolution during the subsequent application of the transport layer may be used; these include, for example, polyamide resins and polyvinyl phosphonic acid.
  • the thickness of an organic intermediate layer may be of the order of magnitude of about 1 ⁇ m while the thickness of a metal oxide intermediate layer may be of the order of magnitude of about 10 2 to 10 4 Angstrom units.
  • the layer of amorphous selenium, or of a mixture of selenium and tellurium, which is adjacent to the carrier material (or to the intermediate layer if one is present), advantageously has a thickness in the range of about 0.1 to about 2 ⁇ m, preferably from about 0.1 to about 1 ⁇ m.
  • the selenium which is advantageously 99.999% pure, may be vapor-deposited in a vacuum of about 10 - 4 to about 10 - 6 mm Hg, from inductively heated quartz crucibles, at a temperature in the range of about 200 to about 280°C.
  • the distance from the substrate which is preferably maintained at a temperature below 40°C, is advantageously 15 to 35 cm.
  • the formation of the homogeneous selenium layer may be followed by means of a thickness measuring instrument (for example QM 310, Film Thickness Monitor, Kronos Inc., Torrance, California). Good photosensitivity is achieved in the thickness range indicated above.
  • the photosensitivity decreases markedly.
  • the selenium layer vapor-deposited in the above way is amorphous.
  • the flash vaporization method under appropriate subatmospheric pressure conditions has proved to be particularly advantageous.
  • a mixed phase preferably containing from about zero to about 45% by weight of tellurium is prepared and comminuted.
  • the granular powder is introduced into a preheated crucible from whence immediate vaporization occurs.
  • the thickness of vapor-deposited selenium-tellurium layers preferably also is within the above-mentioned range.
  • tellurium to the selenium is of assistance because it broadens the sensitivity range of selenium in the red region of the spectrum, as is known, for example, from U.S. Pat. No. 2,745,327.
  • the charge carrier transport layer which is adjacent to the selenium or selenium-tellurium layer, has a high electrical resistance and prevents the dissipation in the dark of the electrostatic charge. Upon exposure to light, it transports the charges produced in the selenium or selenium/tellurium layer. Without the Se or Se-Te layer, it exhibits, in the visible spectral region of about 450 to 750 ⁇ m, a substantially lower photosensitivity.
  • the charge carrier transport layer may be applied by any suitable method, for example by centrifuging, coating, spraying, or dipping.
  • a limit is imposed on the drying conditions that may be used for the charge carrier transport layers because of a modification transformation of selenium at high temperatures.
  • the temperature preferably should not exceed about 90°C if the dwell time of the double layer in the drying zone is only about 1 to 3 minutes.
  • the charge carrier transport layer used according to the invention comprises the oligomeric condensation product, which effects charge transport, and, optionally, a resin binder and/or an adhesion promoter.
  • a resin binder or adhesion promoter used is preferably chosen having regard to the charge transport, film properties, adhesion promotion and surface properties of the compound which effects charge transport.
  • additional sensitizers or materials forming charge transfer complexes can be present. However, these should be employed only to the extent that the requisite transparency of the charge carrier transport layer is not impaired.
  • further additives for example levelling agents, plasticizers and adhesion promoters, also can be present.
  • Suitable compounds which effect charge transfer are above all organic compounds which have an expanded ⁇ -electron system.
  • These include, according to the invention, oligomeric aromatic compounds.
  • the condensation products of formaldehyde and a pyrene having a substituent in at least one of the positions in which reaction can occur, preferably 3-bromopyrene have proved particularly advantageous compared to the previously proposed pyrene, since, as a result of the blocking of one cross-linking position, they make possible linear methylene linkage of the pyrene molecules.
  • the oligomeric condensation product used as the electron donor compound in the materials of the invention is preferably employed alone. However, it also can be used, if desired, in admixture with a resin binder (for example a hydrocarbon resin) and/or further additives.
  • a resin binder for example a hydrocarbon resin
  • Preferable binders are copolymers of polyvinyl chloride and polyvinyl acetate such as Hostaflex M 131 (Farbwerke Hoechst AG) or VYHH, VMCH (Union Carbide Corporation).
  • a plasticizer preferably a halogenated hydrocarbon (for example Hordaflex LC 50 or LC 60 of Farbwerke Hoeschst AG, or Aroclor of Monsanto, USA) or a Clophen resin of Bayer AG, may be employed.
  • a halogenated hydrocarbon for example Hordaflex LC 50 or LC 60 of Farbwerke Hoeschst AG, or Aroclor of Monsanto, USA
  • a Clophen resin of Bayer AG may be employed.
  • the ratio in which the charge-transporting electron donor compound and the resin binder are mixed can vary. Because of the requirement that the maximum possible photosensitivity be obtained, however, a major proportion of the condensation product according to the invention is preferably used in the layer.
  • a suitable mixing ratio is about 2 : 1 parts by weight.
  • the proportion of resin is in the range of about 10 to 20% by weight, based on the weight of the resin/donor compound mixture. It has been found that increasing the proportion of certain resins used as binders increases the residual charge.
  • a sensitizer used in the charge carrier transport layer advantageously may assist the charge transport. In addition, it may produce charge carriers with the electron donor compound.
  • sensitizers it is possible to employ, for example, Rhodamine B extra, Schultz, Farbstoffabellen (Dyestuff Tables), volume I, 7th Edition, 1931, No. 864, page 365, Brilliant Green No. 760, page 314, Crystal Violet, No. 785, page 329, and Kryptocyanin, No. 927, page 397.
  • Compounds which form charge transfer complexes with the charge-transporting compound used according to the invention also can have the same type of effect as a sensitizer. By means of this, a further increase in the photosensitivity of the photoconductive layers of the invention can be achieved.
  • the amount of the added sensitizers or of the compound which forms the charge transfer complex is so chosen that the resulting donor-acceptor complex, with its charge transfer band, is still sufficiently transparent for the purpose of the selenium or selenium/tellurium layer below it.
  • the thickness of the layer also is an important parameter for optimum photosensitivity; layer thicknesses between about 5 and about 30 ⁇ m have proved to be suitable. Layer thicknesses between about 5 and about 15 ⁇ m are particularly advantageous. Quite generally, a lower maximum charge level must be expected at layer thicknesses below about 5 ⁇ m.
  • the materials of the invention make it possible to obtain a high charge coupled with low dark discharge. While with all previously proposed materials an increase in photosensitivity is coupled with an increase in the dark current, the present invention makes it possible to substantially overcome this difficulty. As a result, the materials of the invention can be used both in electrophotographic copying apparatuses of low copying speed and very low lamp energy and in electrophotographic copying apparatuses with high copying speeds and correspondingly higher lamp outputs.
  • Solutions of 3-bromopyrene resin are applied to an amorphous vapor-deposited Se layer of 0.3 ⁇ m thickness which has been applied to a 50 ⁇ m thick polyester film vapor-coated with aluminum in such a way that, after the customary drying conditions (30 to 60 minutes at 60°C), layers approximately 5 to 10 ⁇ m thick are obtained.
  • the 3-bromopyrene resin is obtained by condensation of 3-bromopyrene, melting point 94/5°C (Organic Synthesis, Vol. 48, 1968, St. 30) with formaldehyde in glacial acetic acid. After drying, a homogeneous glossy film, which adheres very well, is obtained.
  • the photosensitivity is measured as follows: The photoconductive layer travels, on a rotating disc, through a charging device (corona setting -6.0 kV, grid 1.1 kV) to an exposure station, where it is exposed to an XBO 150 xenon lamp of Messrs. Osram. A KG 3 heat absorption glass of Messrs. Schott u. Gen./Mainz, and a neutral filter of 15% transparency are placed in front of the lamp so that the light intensity in the plane of measurement is approximately 375 ⁇ W/cm 2 . The charge level (U o ) and the photo-induced light decay curve are recorded oscillographically by means of a transparent probe, using a 610 CR electrometer of Messrs. Keithley Instruments, USA.
  • the photoconductive layer is characterized by the charge level (U o ) and the time (T 1/2 ) after which half the charge (U 1/2 ) is reached.
  • a material (zero layer) of analogous structure without a selenium layer is also measured for comparison. The following values are found:
  • the dark decay ⁇ U D is measured in a Dyntest 90 instrument of Messrs. ECE, Giessen; after reaching the saturation voltage, the charge difference for the dark decay is determined after 2 seconds.
  • the half-life (T 1/2 , msec) for the particular wavelength range is determined, using a negative charge, by exposure to an XBO 150 xenon lamp, in front of which are placed monochromatic filters (line filters, halfwidth 10 to 12 nm, Schott u. Gen./Mainz)
  • the spectral photosensitivity of the layer is obtained by plotting the reciprocal values of the product of the half-life, in seconds, and light intensity I, in ⁇ W/cm 2 , against the wavelength ⁇ in nm.
  • the reciprocal value of T 1/2 . I denotes the light energy, per unit area, which must be incident in order to discharge the layer to half the initial voltage U.
  • the curve obtained is shown as curve 1 in FIG. 3 of the accompanying drawings.
  • the thickness of the top layer is approximately 10 ⁇ m after drying.
  • the layer applied has excellent adhesion.
  • the measurement of the dark decay, carried out according to Example 1, shows that ⁇ U D after 2 sec 70 V.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Photoreceptors In Electrophotography (AREA)
  • Phenolic Resins Or Amino Resins (AREA)
  • Light Receiving Elements (AREA)
US05/488,212 1973-07-16 1974-07-12 Electrophotographic recording material Expired - Lifetime US3982937A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DT2336093 1973-07-16
DE2336093A DE2336093C2 (de) 1973-07-16 1973-07-16 Elektrophotographisches Aufzeichnungsmaterial

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US3982937A true US3982937A (en) 1976-09-28

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US (1) US3982937A (https=)
JP (1) JPS5043934A (https=)
DE (1) DE2336093C2 (https=)
FR (1) FR2238170B1 (https=)
GB (1) GB1472758A (https=)
NL (1) NL7409544A (https=)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4050935A (en) * 1976-04-02 1977-09-27 Xerox Corporation Trigonal Se layer overcoated by bis(4-diethylamino-2-methylphenyl)phenylmethane containing polycarbonate
US4191568A (en) * 1977-03-15 1980-03-04 Ricoh Co., Ltd. Photosensitive material for electrophotography with dye containing overlayer
US4341557A (en) * 1979-09-10 1982-07-27 Kelsey-Hayes Company Method of hot consolidating powder with a recyclable container material
US4346159A (en) * 1977-02-14 1982-08-24 Fuji Xerox Co., Ltd. Photosensitive element for electrophotography
US4378418A (en) * 1979-09-04 1983-03-29 Xerox Corporation Hole injecting contact for overcoated photoreceptors
US4403848A (en) * 1982-02-17 1983-09-13 Xerox Corporation Electronic color printing system

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2621854A1 (de) * 1975-07-01 1977-01-27 Xerox Corp Abbildungselement

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3546085A (en) * 1967-01-30 1970-12-08 Xerox Corp Photoelectrophoretic imaging process and suspension
BE763540A (fr) * 1971-02-26 1971-08-26 Xerox Corp Membre de formation d'image en couches et methode de fabrication.
US3725058A (en) * 1969-12-30 1973-04-03 Matsushita Electric Industrial Co Ltd Dual layered photoreceptor employing selenium sensitizer

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1964817B2 (de) * 1969-12-15 1972-11-16 Matsushita Electric Industrial Co., Ltd., Kadoma, Osaka (Japan) Elektrophotographisches aufzeichnungsmaterial

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3546085A (en) * 1967-01-30 1970-12-08 Xerox Corp Photoelectrophoretic imaging process and suspension
US3725058A (en) * 1969-12-30 1973-04-03 Matsushita Electric Industrial Co Ltd Dual layered photoreceptor employing selenium sensitizer
BE763540A (fr) * 1971-02-26 1971-08-26 Xerox Corp Membre de formation d'image en couches et methode de fabrication.

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4050935A (en) * 1976-04-02 1977-09-27 Xerox Corporation Trigonal Se layer overcoated by bis(4-diethylamino-2-methylphenyl)phenylmethane containing polycarbonate
US4346159A (en) * 1977-02-14 1982-08-24 Fuji Xerox Co., Ltd. Photosensitive element for electrophotography
US4191568A (en) * 1977-03-15 1980-03-04 Ricoh Co., Ltd. Photosensitive material for electrophotography with dye containing overlayer
US4378418A (en) * 1979-09-04 1983-03-29 Xerox Corporation Hole injecting contact for overcoated photoreceptors
US4341557A (en) * 1979-09-10 1982-07-27 Kelsey-Hayes Company Method of hot consolidating powder with a recyclable container material
US4403848A (en) * 1982-02-17 1983-09-13 Xerox Corporation Electronic color printing system

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FR2238170B1 (https=) 1976-10-22
NL7409544A (nl) 1975-01-20
GB1472758A (en) 1977-05-04
DE2336093C2 (de) 1983-05-26
FR2238170A1 (https=) 1975-02-14
AU7116774A (en) 1976-01-15
JPS5043934A (https=) 1975-04-21
DE2336093A1 (de) 1975-02-06

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